The ghoul is linked with both the vampire and the werewolf in traditional folklore, but there are a number of obvious reasons why the entity has never attained the popularity achieved by the Frankenstein monsters, Draculas, and Wolfmen of the horror films. The category of ghoul encompasses a number of different entities. One type of ghoul, like the vampire, is a member of the family of the undead, continually on the nocturnal prowl for new victims. Unlike the vampire, however, this ghoul feasts upon the flesh of the deceased, taking the corpses from cemeteries and morgues. The ghoul more common to the waking world is that of the mentally unbalanced individual who engages in eating or otherwise desecrating the flesh of deceased humans. Yet a third type of ghoul would be those native of Arabic folklore, the ghul (male) and ghulah (female), demonic jinns that haunt burial grounds and sustain themselves on human flesh stolen from graves.
It is easy to envision how the legend of the ghoul began in ancient times when graves were shallow and often subject to the disturbances of wild animals seeking carrion. Later, as funeral customs became more elaborate and men and women were buried with their jewelry and other personal treasures, the lure of easy wealth superseded any superstitious or ecclesiastical admonitions that might have otherwise kept grave robbers away from cemeteries and from desecrating a corpse's final rest.
Then, in the late 1820s, surgeons and doctors began to discover the value of dissection. The infant science of surgery was progressing rapidly, but advancement required cadavers— and the more cadavers that were supplied, the more the doctors realized how little they actually knew about the anatomy and interior workings of the human body, and thus the more cadavers they needed. As a result, societies of grave robbers were formed called the "resurrectionists." These men made certain that the corpses finding their way to the dissecting tables were as fresh as possible. And, of course, digging was easier in unsettled dirt. The great irony was that advancement in medical science helped to perpetuate the legend of the ghoul.